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      <title>最长回文子串 - 交互式测验</title>
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    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>最长回文子串 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
                    <div class="progress-bar">
                        <div id="progress-indicator"></div>
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                    <div id="question-container">
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                  <button id="next-btn" class="nav-btn">下一题</button>
                </div>
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      </div>

      <script>
        const quizData = [
  {
    "question": "根据CAP理论，当分布式系统中发生网络分区（Partition）时，系统设计者通常需要在以下哪两个特性之间做出权衡？",
    "options": [
      "一致性 (Consistency) 和持久性 (Durability)",
      "可用性 (Availability) 和原子性 (Atomicity)",
      "一致性 (Consistency) 和可用性 (Availability)",
      "分区容错性 (Partition tolerance) 和一致性 (Consistency)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "CAP理论的核心在于，任何分布式系统最多只能同时满足三项中的两项。由于网络分区（P）在分布式环境中是不可避免的，因此必须保证。这就迫使我们在一致性（C）和可用性（A）之间做出选择。选择C，就意味着在分区期间，为保证数据一致性，部分节点可能需要停止服务，牺牲A。选择A，就意味着在分区期间，为保证服务可用，节点可能返回旧数据，牺牲了C。",
    "source": "文档中「1. 理论基础 - CAP 定理」部分",
    "hint": "文档提到：“在分布式系统中，分区容错性（P）是必须保证的基础。因此，架构师的挑战通常是在一致性（C）和可用性（A）之间进行权衡。”"
  },
  {
    "question": "两阶段提交协议（2PC）最主要的缺点是什么，这可能导致系统出现严重问题？",
    "options": [
      "实现过于简单，无法处理复杂场景",
      "只支持最终一致性，无法保证数据强一致性",
      "缺乏协调者角色，导致事务难以管理",
      "同步阻塞问题，协调者或参与者故障可能导致资源长时间锁定"
    ],
    "correctAnswerIndex": 3,
    "explanation": "2PC最大的问题在于其同步阻塞机制。在第一阶段（准备阶段）结束后，所有参与者都在等待协调者的最终指令（提交或回滚）。如果此时协调者宕机，参与者将无法收到指令，导致它们占有的资源被无限期锁定，从而影响整个系统的可用性。",
    "source": "文档中「2.1 两阶段提交 (2PC) - 缺点」部分",
    "hint": "考虑一下，在第一阶段所有参与者都回复“准备好了”之后，如果协调者突然失联，会发生什么情况？"
  },
  {
    "question": "在TCC（Try-Confirm-Cancel）模式中，“Try”阶段的核心职责是什么？",
    "options": [
      "直接提交业务操作，完成数据写入",
      "检查业务可行性并预留必要的业务资源",
      "执行与Try阶段相反的操作，释放预留的资源",
      "异步通知其他系统事务已开始"
    ],
    "correctAnswerIndex": 1,
    "explanation": "TCC模式的精髓在于将一个大的事务操作拆分为三个独立的阶段。'Try'阶段并不执行真正的业务操作，而是进行业务检查（如检查库存、账户余额）并预留资源（如冻结库存、冻结金额）。这个阶段的成功是后续'Confirm'阶段能够顺利执行的前提。",
    "source": "文档中「3.1 TCC (Try-Confirm-Cancel)」部分",
    "hint": "文档中描述 'Try' 阶段时提到：“完成所有业务检查...预留必要的业务资源。”"
  },
  {
    "question": "Saga模式是如何实现事务回滚的？",
    "options": [
      "通过全局锁，在出错时阻止所有后续操作",
      "依赖数据库的原子性提交功能",
      "为每个成功的子事务执行对应的补偿操作",
      "等待协调者超时后，自动撤销所有操作"
    ],
    "correctAnswerIndex": 2,
    "explanation": "Saga模式不使用传统的数据库锁或全局事务来实现回滚。它的核心思想是“补偿”。如果长事务中的某个子事务失败，Saga会按照相反的顺序，依次调用所有已经成功执行的子事务的“补偿操作”，从而在业务逻辑上抵消之前操作的影响，达到最终一致的状态。",
    "source": "文档中「3.2 Saga 模式」部分",
    "hint": "当一个长流程中的某个步骤失败时，Saga需要“撤销”已经完成的步骤。这个“撤销”在Saga中被称为..."
  },
  {
    "question": "与ACID模型的强一致性相比，BASE理论的核心思想是什么？",
    "options": [
      "基本可用 (Basically Available)，软状态 (Soft state)，最终一致性 (Eventually consistent)",
      "原子性 (Atomicity)，一致性 (Consistency)，隔离性 (Isolation)，持久性 (Durability)",
      "强可用性 (Always Available)，硬状态 (Hard state)，立即一致性 (Immediately consistent)",
      "业务聚合 (Business Aggregation)，同步执行 (Synchronous Execution)，早期确认 (Early Commit)"
    ],
    "correctAnswerIndex": 0,
    "explanation": "BASE理论是面向高可用、大规模分布式系统的设计思想，它牺牲了强一致性来换取更高的可用性。其核心是：基本可用（Basically Available）指系统在出现故障时，允许损失部分可用性；软状态（Soft state）指允许系统中的数据存在中间状态；最终一致性（Eventually consistent）指系统中的所有数据副本在经过一定时间后，最终能够达到一致的状态。",
    "source": "文档中「1. 理论基础 - BASE 理论」部分",
    "hint": "BASE是三个英文单词的首字母缩写，这三个单词精确地描述了其核心理念。"
  },
  {
    "question": "在Saga模式的两种实现方式中，“编排模式 (Orchestration)”与“协同模式 (Choreography)”最根本的区别在于？",
    "options": [
      "编排模式性能更高，协同模式可靠性更强",
      "编排模式有无一个中央协调器来控制流程",
      "编-c-编排模式只适用于同步调用，协同模式只适用于异步消息",
      "只有协同模式才支持补偿事务"
    ],
    "correctAnswerIndex": 1,
    "explanation": "最核心的区别在于是否存在一个明确的“指挥者”。在编排模式中，有一个中央协调器（Orchestrator）负责调用各个参与者服务，并根据结果决定下一步做什么（继续、补偿或结束），流程控制是集中的。而在协同模式中，没有中央协调器，每个服务完成自己的工作后会发布一个事件，其他服务监听这些事件并触发自己的后续操作，服务间的协作是去中心化的。",
    "source": "文档中「3.2 Saga 模式 - 实现方式」部分",
    "hint": "想象一下交响乐团的指挥和一支爵士乐队的即兴合奏，哪一个更像编排模式？"
  },
  {
    "question": "“基于可靠消息的最终一致性方案”主要解决了什么问题？",
    "options": [
      "实现了跨多个数据库的实时、强一致性事务",
      "确保了本地事务执行与消息发送这两个操作的原子性",
      "消除了分布式系统中的网络延迟",
      "完全替代了TCC和Saga模式，成为唯一的解决方案"
    ],
    "correctAnswerIndex": 1,
    "explanation": "该方案的核心挑战在于如何保证“业务操作”和“发送消息”这两个步骤要么都成功，要么都失败。如果业务操作成功但消息没发出去，下游系统将无法感知变化；如果业务操作失败但消息发出去了，下游系统会处理一个本不该发生的操作。因此，该方案通过本地消息表、事务消息等机制，确保了这两个操作的原子性，从而为最终一致性打下可靠基础。",
    "source": "文档中「3.3 基于可靠消息的最终一致性方案」部分",
    "hint": "思考一下，在执行完数据库更新后，但在发送消息到MQ之前，服务突然崩溃了，会引发什么问题？这个方案就是为了解决这类问题。"
  }
];
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                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  